This invention relates to fluid power systems and more particularly to a free-standing structural unit for use with such systems that include a variable displacement hydraulic transmission.
Variable displacement hydraulic transmissions have now been commercially available for many years. Such devices are powered by a prime mover such as an electric motor, a turbine, or an internal combustion engine, and are capable of converting the constant speed shaft work input to a variable pressure, variable flow rate hydraulic output. These devices include a hydraulic, pneumatic, or electrical control device such as a stroker or servo mechanism through which the hydraulic flow rate can be varied from zero to maximum output. Transmissions of this type are well suited for use in powering a large variety of industrial hydraulically actuated tools and equipment because they allow power to be transmitted to remote locations without a mechanical power train, in either forward or reverse directions, at variable speed and/or variable torque. Further, they can provide dynamic breaking effects, an infinite number of hydraulic ratios (which allow engine power to be precisely matched to load conditions), and are not damaged when temporarily overloaded.
Such systems require a number of components in addition to the prime mover, the transmission, and associated hydraulic lines. Typical systems include a hydraulic fluid reservoir, a suction filter, and a heat exchanger. Preferably, a vacuum switch is included in the line between the suction filter and the transmission's charge pump to warn the operator when the suction filter is clogged. The high pressure lines which communicate between the transmission and the hydraulically driven device should each include a relief valve. Other components found in such systems include a shuttle valve installed in parallel with the transmission to provide for removal of the hot oil from the system, a pressure line filter, line pressure indicating devices, and flow turbines which read fluid flow rate.
As with most devices, hydraulic devices often have an exterior enclosure that supports component parts of the device and shields those components from damage. For example, U.S. Pat. No. 2,390,620 discloses a small, portable hydraulic driving device, and U.S. Pat. No. 2,662,375 describes a hydraulic transmission, both of which have conventional exterior enclosures. It is also known to provide a housing that serves additional functions such as noise reduction or storage or doubles as a housing for a hydraulic pump and a reservoir, in which case the pump is immersed in the oil. U.S. Pat. No. 3,885,892, for example, describes a specialized housing for a portable air compressor that reduces noise and vibration, has a built-in hose storage capability, and promotes both cool operation and handling convenience.
A complete system of the type described above necessarily includes a prime mover, a hydraulic pump, a hydraulically driven motor, and a machine driven by the motor. Heretofore, hydraulic systems have usually been individually designed to meet the requirements of a specific use, but subcombinations of the foregoing basic components, packaged as a unit together with associated filters, reservoir, and the like, on a skid or within an enclosure have also been available. A common example is a hydraulic power plant consisting of a prime mover and a hydraulic pump, packaged together to provide hydraulic power to several alternately used machine tools. Such systems are restricted to one prime mover, a single type of power coupling, and usually well defined output requirements. In particular, the transmission component of the system is usually designed to be driven by a specific prime mover, e.g., a diesel engine of a certain horsepower, and in turn to drive a specific hydraulic device or devices. In short, such subcombinations of components lack versatility.
Another commercially available combination of hydraulic components is the so-called "hydraulic transmission" consisting of a hydraulic pump, a hydraulically powered rotary motion device, and their associated equipment, packaged as a single unit. These are used, for example, in vehicle propulsion systems to transmit power from a diesel engine to the wheels.
In addition to a marked lack of versatility, the known systems have failed to solve the problem of simultaneously satisfying competing demands of containment and accessibility imposed on an exterior housing for a system that includes a hydraulic transmission. More specifically, it is highly desirable to contain leaks of hydraulic fluid or, more importantly for the safety of personnel working near the system, leaks or an explosion that could spray extremely hot oil carried at pressures typically in excess of thousands of p.s.i. On the other hand, it is also important to have ready access to the system for maintenance (such as the changing of filters), control, and monitoring of its functioning. The aforementioned "open" skid arrangement represents a choice in favor of accessibility and mobility at the expense of containment, safety, and compactness. More generally, no prior art system known to applicant provides a highly versatile hydraulic interface between a prime mover and a hydraulically driven device that contains leaks and explosions, and is compact, while at the same time providing a high degree of accessibility for regular maintenance, control, monitoring, and inspection.